The dynamic regulation of chromatin serves as an important mechanism for gene regulation. Many studies have demonstrated that posttranslational modification such as acetylation, phosphorylation, ubiquitination, and/or methylation of histones is a mechanism that regulates the chromatin environment and gene expression profiles. Many of these histone modifying activities, when disrupted (i.e., mutations, amplifications and chromosomal translocations), are associated with human cancers. Therefore, studying the machinery that mediates these modifications will provide us with a better understanding of how eukaryotic genomes are regulated and how mis-regulation of these modifying activities can lead to human diseases. The long-term objective of this proposal is to understand the biological role of Set1, the budding yeast histone H3 Lys4 methyltransferase, and its associated proteins in gene regulation. To achieve this goal we will use a combination of molecular, biochemical and genetic approaches to determine the importance of Set1-associated proteins in histone methylation, identify novel Set1-associated proteins, and characterize the functional domains of Set1 that regulate methyltransferase activity. Understanding the basic function of Set1 and Set1-associated proteins and how they mediate H3 Lys4 methylation will provide further mechanistic insight into how Set1 mediates gene regulation such as transcriptional activation, elongation and/or silencing. Finally, we predict that results from our studies will have wide implications since many SET domain-containing proteins exist in other organisms such as plants, insects and animals. Furthermore, several Set1 H3 Lys4 methyltransferase human homologues exist (e.g., MLL1, MLL2, and Set9) and have been associated with cancers. Therefore, understanding how Set1 functions in yeast may provide key insights into understanding how SET domain-containing methyltransferases lead to human diseases such as cancer.